Sometimes being healthy requires an arduous discipline, but making and eating fresh homemade yogurt is one of the fun parts about good health. Below are the materials I use to make yogurt.
I prefer using an electric yogurt maker, but it is possible to make yogurt without one as many cultures have for centuries. The main ingredient is fresh milk. Organic whole milk is best if you can get it, but any milk will do that does not have antibiotics in it which can kill the organisms. Even UHT milk or powdered milk can work. I prefer to add about 1/2 cup of cream (125mL) to one quart (1 liter) of milk to make it richer, but the amount of milk fat is personal preference.
Yogurt makers can have one large bowl or several individual one serving size containers. I prefer one that has a large glass bowl, but stainless steel or plastic will also work. For best results, I sterilize the bowl with boiling water. Then, I fill it with the milk and cream mixture and place it the microwave. Through trial and error and use of a food thermometer, bring the milk to about 180-200° F (92-95° C). This serves two functions, it sterilizes the milk so there are no unwanted bacteria giving it an off taste, and it slightly modifies the milk so it is smoother when it ferments and does not curdle.
Using a food thermometer, let the milk cool to 108-112° F (42-44° C). Usually, a skin will form on the surface. Many people skim this off. It is milk protein and I prefer to blend it back in with a little battery powered hand blender. At this point, you may add one packet of probiotic yogurt starter. I picture the Yógourmet brand probiotic yogurt starter above which has five strains including the two normal yogurt strains and three probiotic strains. You can read about it here. There are several good probiotic yogurt starters in China but they are formulated to make a thinner drinking yogurt. I use two packets of the Chinese yogurt starters to get a thicker yogurt.
As you can see from the above chart, the length of the fermentation will affect (1) the amount of carbohydrate in the form of lactose (milk sugar), (2) the sourness of the yogurt determined by the amount of lactic acid, and (3) the amount of live micro-organisms. Commerical yogurt is only fermented for 4-5 hours. Most people ferment home yogurt for 8-10 hours. The Specific Carbohydrate Diet for people with autoimmune diseases recommends fermenting yogurt for a full 24 hours and then straining it to get the lowest possible lactose content as lactose is a potent allergen for many people. I generally ferment my yogurt for 20-24 hours to get the most probiotic organisms and the lowest carbohydrate. I like the tarter taste of a fully fermented yogurt, but some may prefer a more mild taste.
Dripping or straining yogurt will make it thicker and change the composition. Traditionally, cheese cloth is used to strain it, but I prefer to use a simple paper coffee filter or a reusable nylon coffee filter which I place in a cylindrical container to catch the liquid which drips off. The liquid portion that drips off will contain water, lactic acid and some residual lactose. Very little micro-organisms, protein or fat will drip through. A dripped yogurt will be slightly less sour, much thicker, lower carb (less lactose), higher protein and have more concentrated probiotic organisms.
If you drip the yogurt for about an hour, you will reduce the volume about 25% and get thicker Greek style yogurt. If you drip the yogurt over night in the refrigerator, you will reduce the volume over 50% and you will get thick yogurt cheese, which is almost like cream cheese in taste and usage.
Remember that yogurt is a live food and be sure to eat it fresh. Even when stored in the refrigerator, it can lose more than half of the live organisms within a week. And it tastes great fresh!